Golang Position.Offset方法代码示例

// NewCommentMap creates a new comment map by associating comment groups
// of the comments list with the nodes of the AST specified by node.
//
// A comment group g is associated with a node n if:
//
//   - g starts on the same line as n ends
//   - g starts on the line immediately following n, and there is
//     at least one empty line after g and before the next node
//   - g starts before n and is not associated to the node before n
//     via the previous rules
//
// NewCommentMap tries to associate a comment group to the "largest"
// node possible: For instance, if the comment is a line comment
// trailing an assignment, the comment is associated with the entire
// assignment rather than just the last operand in the assignment.
//
func NewCommentMap(fset *token.FileSet, node Node, comments []*CommentGroup) CommentMap {
	if len(comments) == 0 {
		return nil // no comments to map
	}

	cmap := make(CommentMap)

	// set up comment reader r
	tmp := make([]*CommentGroup, len(comments))
	copy(tmp, comments) // don't change incoming comments
	sortComments(tmp)
	r := commentListReader{fset: fset, list: tmp} // !r.eol() because len(comments) > 0
	r.next()

	// create node list in lexical order
	nodes := nodeList(node)
	nodes = append(nodes, nil) // append sentinel

	// set up iteration variables
	var (
		p     Node           // previous node
		pend  token.Position // end of p
		pg    Node           // previous node group (enclosing nodes of "importance")
		pgend token.Position // end of pg
		stack nodeStack      // stack of node groups
	)

	for _, q := range nodes {
		var qpos token.Position
		if q != nil {
			qpos = fset.Position(q.Pos()) // current node position
		} else {
			// set fake sentinel position to infinity so that
			// all comments get processed before the sentinel
			const infinity = 1 << 30
			qpos.Offset = infinity
			qpos.Line = infinity
		}

		// process comments before current node
		for r.end.Offset <= qpos.Offset {
			// determine recent node group
			if top := stack.pop(r.comment.Pos()); top != nil {
				pg = top
				pgend = fset.Position(pg.End())
			}
			// Try to associate a comment first with a node group
			// (i.e., a node of "importance" such as a declaration);
			// if that fails, try to associate it with the most recent
			// node.
			// TODO(gri) try to simplify the logic below
			var assoc Node
			switch {
			case pg != nil &&
				(pgend.Line == r.pos.Line ||
					pgend.Line+1 == r.pos.Line && r.end.Line+1 < qpos.Line):
				// 1) comment starts on same line as previous node group ends, or
				// 2) comment starts on the line immediately after the
				//    previous node group and there is an empty line before
				//    the current node
				// => associate comment with previous node group
				assoc = pg
			case p != nil &&
				(pend.Line == r.pos.Line ||
					pend.Line+1 == r.pos.Line && r.end.Line+1 < qpos.Line ||
					q == nil):
				// same rules apply as above for p rather than pg,
				// but also associate with p if we are at the end (q == nil)
				assoc = p
			default:
				// otherwise, associate comment with current node
				if q == nil {
					// we can only reach here if there was no p
					// which would imply that there were no nodes
					panic("internal error: no comments should be associated with sentinel")
				}
				assoc = q
			}
			cmap.addComment(assoc, r.comment)
			if r.eol() {
				return cmap
			}
			r.next()
		}
//.........这里部分代码省略.........

// Verify that calling Scan() provides the correct results.
func TestScan(t *testing.T) {
	whitespace_linecount := newlineCount(whitespace)

	// error handler
	eh := func(_ token.Position, msg string) {
		t.Errorf("error handler called (msg = %s)", msg)
	}

	// verify scan
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(source)), source, eh, ScanComments|dontInsertSemis)

	// set up expected position
	epos := token.Position{
		Filename: "",
		Offset:   0,
		Line:     1,
		Column:   1,
	}

	index := 0
	for {
		pos, tok, lit := s.Scan()

		// check position
		if tok == token.EOF {
			// correction for EOF
			epos.Line = newlineCount(string(source))
			epos.Column = 2
		}
		checkPos(t, lit, pos, epos)

		// check token
		e := elt{token.EOF, "", special}
		if index < len(tokens) {
			e = tokens[index]
			index++
		}
		if tok != e.tok {
			t.Errorf("bad token for %q: got %s, expected %s", lit, tok, e.tok)
		}

		// check token class
		if tokenclass(tok) != e.class {
			t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
		}

		// check literal
		elit := ""
		switch e.tok {
		case token.COMMENT:
			// no CRs in comments
			elit = string(stripCR([]byte(e.lit)))
			//-style comment literal doesn't contain newline
			if elit[1] == '/' {
				elit = elit[0 : len(elit)-1]
			}
		case token.IDENT:
			elit = e.lit
		case token.SEMICOLON:
			elit = ";"
		default:
			if e.tok.IsLiteral() {
				// no CRs in raw string literals
				elit = e.lit
				if elit[0] == '`' {
					elit = string(stripCR([]byte(elit)))
				}
			} else if e.tok.IsKeyword() {
				elit = e.lit
			}
		}
		if lit != elit {
			t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, elit)
		}

		if tok == token.EOF {
			break
		}

		// update position
		epos.Offset += len(e.lit) + len(whitespace)
		epos.Line += newlineCount(e.lit) + whitespace_linecount

	}

	if s.ErrorCount != 0 {
		t.Errorf("found %d errors", s.ErrorCount)
	}
}